a) Field of the Invention
This invention relates to a modular pressure relief valve arrangement in a limited slip differential or torque coupling device for use with a vehicle drive train, for example, a speed sensitive limited slip differential; and more particularly is directed a removable modular valve assembly for a hydraulically actuated clutch pack in such a limited slip device.
b) Background of Related Art
Limited slip differentials, or torque coupling devices are well known in the art. In such limited slip devices, a hydraulically actuated friction clutch pack is actuated to retard relative rotation of at least one of the side gears relative to the differential case. Normally, hydraulic pressure is directly increased in response to an increase in rotational speed differential of the axle gears. One common way to provide the hydraulic pressure is to include an internal pump, or gerotor pump, within the differential case. As hydraulic pressure increases as a result of the increased speed of the pump (increased speed differential between one output shaft and the different case) there is a need to provide a pressure relief valve to provide relief from pressure build up in the limited slip device. In other words, once the hydraulic pressure reaches a predetermined level, the pressure relief valve relieves that pressure.
One such pressure relief valve of the related art is shown in FIG. 4. A ball is simply provided in a ball seat on the external surface of the differential case. The ball seat is in communication with hydraulic fluid of the limiting device. The ball is retained in the seat by a leaf spring secured to the outer surface of the differential case. As hydraulic pressure in the limiting device increased, the ball is forced against the leaf spring. If sufficient pressure exists, the leaf spring opens and fluid is allowed to flow out of the differential case. Otherwise, the valve remains closed. However, while this type of leaf spring ball valve does relieve excessive pressures, it suffers from the drawback that too many variables effect the opening and closing of the valve. During operation of the differential assembly, the related art valve does not predictably open and close consistently as desired.
The need therefore exists for an improved differential relief valve that is simple in design, easy to assembly and opens and closes in a predictable and consistent manner.
The present invention provides an improved pressure relief valve for use in a limited slip differential or torque coupling device. A modular pressure relief valve assembly is removably disposed in the differential case and is connected to a passageway leading to a limited slip device within the differential case to establish fluid communication there between.
When pressure within the differential case or limited slip device exceeds a predetermined pressure, the ball is lifted from the valve seat and fluid passes through the differential case to an exterior within the differential housing. When pressure in the differential case and limited slip device is less than the pre-determined pressure, fluid is prevented from passing through the valve.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.